Silver-magnesium contact



Patented June 6, 1939 mvaa-rssonssmu .cou'rscr I'ransllenselandlennethhllmmert,lndianapelialndsasslgnerstck l llailory &

- Isuiiassapoih, Int. a corporation of iclaim.

This invention relates to electric contacts. The present invention constitutes an improvement on the invention set forth in co-pending application Serial #223,506. a An object of the invention is to improve the characteristics of theelectric contact elements containing silver.

Another object of the invention is to "provide" 'a silver base contact material, which will retain 10 a very low contact resistance.

A' still further object is to provide a new contact material which can be .used under'severe electrical loads, without welding or sticking.

It is a further object of the invention to profled in the disclosure hereinafter'set forth, the

scope of the invention being indicated in the 25 appended claims.

While a'preferred embodiment of the invention is described herein, it is contemplated that a considerable variation may be made in the method of procedure, and the combination of elements, without departing from the spirit of the invention.

The present invention comprises an.improve-- ment in silver-base electric contact elements.

According to the invention, the contacts are 35 improved by the addition of small percentages of ms'nesium.

The contacts are composed of silver and magnesium, the ingredients being present in the following proportions:

Magnesium "per cent-.. ltoSJ Silver Balance We. have discovered that contact alloys of 2 to 3.8% magnesium exhibit a surprising increase in 5 current carrying or interrupting capacity. The

greatest current capacity appears to be achieved with alloys containing 3 to 8.6% magnesium. In

comparative tests contacts of this composition withstood 2'1 amperes without welding together sq while interrupting a 12 volt D. C. circuit at a frequency of 470 cycles per second. Contacts of ilne silver, similarly tested had a critical current value of 12 amperes and those of coin silver a current value of 11 amperes under the same 55 conditions.

Itisalsofcundthatthe 'amountofmaterial mm Serial No. 1,727

. .to 3.8%. magnesium and the balance silver.

larch 1s, 1m,

transfer from contact to contact during operation is very low with this composition.

The electrical conductivity of the alloy likewise decreases rapidly above the range of com- P sitions described. 6

The contact resistance of the present alloy is as low as that of finesilver and some compositions are even lower. The alloy has a definite advantage that the contact resistance values are not erratic, but very constant. It is often 10 found with other contact alloys that in service,

a high contact resistance will be built up after a short period of operation, and if the contacts continuein operation, the contact resistance might drop down again to lower values, and vary 16' as much as 10 miiliohms. Such is also the case with line silver.

An outstanding advantage of the alloys with the limited range of compositions, as given above. is that materials of this type can be easily swaged 90 and drawn into the form oi wires or rolled into. the form of sheet, from which contacts may be prepared by a punching operation, screw machine operation, cold heading, and the like. The alloyhes an electrical conductivity of to I. A. C. S. and similar-b high thermal conductiv ity which is important, because it will prevent over-heating of the contacts.

The new silver-magnesium alloy can readily be prepared in the form of contact bi-metak, in '0 which one side consists of a base metal and the other side of the silver-magnesium alloy.

While the present invention as to its objects and advantages has been described herein, as carried out in specific embodiments thereof, it is not desired to be limited thereby, but it a intended to cover the invention broadly, within the spirit and scope of the appended claims.

What is claimed is: a

1. An electric contact formed of an alloy of 2 2. An electric contact formed of an alloy of 8 to 3.6% magnesium and the balance silver.

3. An electric contact formed of an alloy of 2 to 3.8% magnesium and the balance substan- 

